The tapetum and systematics in monocotyledons

This paper critically reviews the homologies and distribution of tapetum types in monocotyledons, in relation to their systematics. Two main types of tapetum are widely recognised: secretory and plasmodial, although intermediate types occur, such as the “invasive” tapetum described inCanna. In secretory tapeta, a layer of cells remains intact around the anther locule, whereas in the plasmodial type a multinucleate tapetal plasmodium is formed in the anther locule by fusion of tapetal protoplasts. In invasive tapeta, the cell walls break down and tapetal protoplasts invade the locule without fusing to form a plasmodium. When examining tapetum type, it is often necessary to dissect several developmental stages of the anthers. Secretory and plasmodial tapeta are both widely distributed in monocotyledons and have probably evolved several times, although there may be some systematic significance within certain groups. Among early branching taxa,Acorus andTofieldia have secretory tapeta, whereas Araceae and Alismatales are uniformly plasmodial. The tapetum is most diverse within Commelinanae, with both secretory and plasmodial types, and some Zingiberales have an invasive tapetum. Lilianae (Dioscoreales, Liliales, and Asparagales) are almost uniformly secretory.     

Systematics and evolutionary biology of the fern genusHymenasplenium (Aspleniaceae)

In Aspleniaceae,Hymenasplenium is a well-defined group with dorsiventral creeping rhizomes. Members ofHymenasplenium are widely distributed in the tropic zones of the world and have great variation in morphology and ecolgy, making it a good model group for plant systematics and evolutionary biology. I have worked on this group using techniques such as comparative morphology, ecology, cytology (for examining chromosomes and reproductive modes), phytochemistry and molecular biology. I considered the evolution of various phenetic characters based on a molecular phylogenetic tree which I recently obtained from sequence comparisons ofrbcL. In this paper, I will summarize the results. Recipient of the Botanical Society Award for Young Scientists, 1993.     

Nomenclatural adjustments in some European monocotyledons

New nomenclatural combinations are validated for fifteen taxa belonging to the generaDanthonia, Stipa, Lolium, Phippsia, Elymus, Schoenoplectus andAllium.     

Alternative modes of leaf dissection in monocotyledons

Although a majority of monocotyledons have simple leaves, pinnately or palmately dissected blades are found in four orders, the Alismatales, Pandanales, Dioscoreales and Arecales. Independent evolutionary origins of leaf dissection are indicated by phylogenetic analyses and are reflected in the diversity of mechanisms employed during leaf development. The mechanism of blastozone fractionation through localized enhancement and suppression of growth of the free margin of the leaf primordium occurs in the Araceae and Dioscoreaceae. By contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through intercalary growth in a submarginal position and, second, the initially simple leaf blade is dissected through an abscission-like process of leaflet separation. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. In this mode, discrete patches of cells undergo programmed cell death during lamina development, resulting in formation of open perforations. When perforations are positioned near the leaf margin, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. Whereas blastozone fractionation defines the early primary morphogenesis phase of leaf development, the other two modes occur later, during the secondary morphogenesis/histogenesis phase. Evolution of these mechanisms presumably has involved recruitment of other developmental programmes into the development of dissected leaves.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 25–44.     

Lateral meristems and stem thickening growth in monocotyledons

Although monocotyledons lack a vascular cambium of the type found in dicotyledons and conifers, lateral meristems still play an important role in the establishment of their growth habits. The presence near the shoot apex of a primary thickening meristem (PTM), which is probably plesiomorphic in monocotyledons, predisposes evolution into the many pachycaul forms. A PTM occurs in virtually all monocotyledons, whereas the secondary thickening meristem (STM), which is morphologically similar, is limited to a few genera of Liliiflorae. these records are reviewed in a systematic context. To a greater or lesser extent in different taxa, the PTM is responsible for primary stem thickening, adventitious root production, and formation of linkages between stem, root and leaf vasculature. The STM largely contributes to the body of the stem. The sometimes obscure distinction between the two meristems, and their relationship with other stem meristems are discussed. For systematic purposes stem thickening in monocotyledons is separated into two characters: diffuse growth (as in palms), and growth by means of lateral meristems. The three states of the second character are represented by the first three of Mangin’s (1882) four categories (two herbaceous, the third arborescent): (1) The lateral meristem is limited in extent, and ceases activity after root formation. (2) It remains active for a limited period after cessation of root formation, contributing to the plant body. (3) It remains active throughout the life of the plant, contributing the bulk of the plant body.     

Lipid metabolism in green leaves of developing monocotyledons

Lipid synthesis was studied in successive leaf sections from the base to the tip of developing barley (Hordeum vulgare L.), maize (Zea mays L.), rye grass (Lolium perenne L.) and wheat (Triticum aestivum L.) leaves. The endogenous levels of acyl lipids and their constituent fatty acids from the same leaf sections were also analysed. The principle chloroplast acyl lipids showed a relative increase in amount with the age of the leaf section. Their content of -linolenic acid also increased whereas there was little change in the amount of this acid in phosphatidylcholine and phosphatidylethanolamine, which are primarily non-chloroplastic. The content of trans-3-hexadecenoic acid in phosphatidylglycerol increased approximately 20-fold between the youngest (basal) and oldest (distal) leaf sections.The incorporation of [¹⁴C]acetate was always high into monogalactosyldiacylglycerol, phosphatidylcholine and the neutral lipid (mainly pigments) fractions. With increasing age, the neutral lipids were less well labelled. In three of the plant species but not in barley, phosphatidylglycerol was heavily labelled. Monogalactosyldiacylglycerol usually contained the highest amount of radioactivity in the middle leaf sections. Apart from these generalisations, each plant type had its own specific pattern of radiolabelling.     

Systematic root anatomy of Asparagales and other monocotyledons

Root anatomy of several taxa of Asparagales and some taxa formerly included in Asparagales is described in a systematic context together with a literature review. The presence of a dimorphic outer layer with long and short cells is widespread in monocotyledons, indicating that it originated early in the monocot lineage, but whereas this layer is rhizodermal in most monocotyledons, in Asparagales and Araceae it is usually hypodermal. There may be a correlation between the presence of a velamen or a persistent rhizodermis in many Asparagales and Araceae and the presence of a dimorphic hypodermal layer. Many other root anatomical characters, such as the presence of vascular bundles in the central pith and a multi-layered sclerenchymatous cylinder, are probably xeromorphic and developed convergently.     

The Nucellus and Chalaza in monocotyledons: Structure and systematics

The majority of monocotyledons are crassinucellate, including some early-branching taxa (sensu Chase et al., 1995a, 1995b) such asTofieldia, although Araceae are predominantly tenuinucellate. The tenuinucellate condition occurs in a taxonomically wide range of monocotyledons, and there is some congruence between this character and existing monocot topologies at higher levels. For example, present evidence indicates a few tenuinucellate asparagoid clades, including Alliaceae sensu stricto and Hypoxidaceae, possibly two tenuinucellate lilioid lineages, and at least two tenuinucellate commelinoid lineages. Proximal nucellar structures arise from a multi-layered region of the ovule and include hypostase, enlarged dermal cells and conducting passage (Zuleitungsbahn), haustoria, postaments, podia, and perisperm. In some cases they may represent the same tissues at different developmental stages; in general the last three are seed structures. For example, a postament may be a resistant conducting passage from which the surrounding dermal cells have degenerated, or alternatively a resistant hypostase, although both are nucellar in origin. Such terminological confusions cause problems in establishing homologies. Several characters relating to the nucellus are outlined.     

Triaperturate pollen in the monocotyledons: configurations and conjectures

Triaperturate pollen are known in at least twenty seven genera of monocotyledons. Differences between aperture type and polarity indicate that the development of three apertures has occurred a number of times. Mode of cytokinesis during microsporogenesis is compared with differences in aperture configuration, to assess the extent to which this appears to influence aperture arrangement. Triapertury in monocot pollen tends to fall into one or another of three situations: 1) it is the normal state, 2) it is fairly common, but pollen with more or less apertures also occur in the taxon or sample, 3) it is a rare, or abnormal state for pollen which usually has less than three apertures. The various forms of triaperturate pollen are described, as well as monosulcate pollen of the orchid genera Cypripedium and Paphiopedilum, often misinterpreted as tri-sulcate, and the unusual extended trichotomosulcate pollen of Agrostocrinum (Hemerocallidaceae). Monosulcy, trichotomosulcy, and zonasulcy, with unusual and rare exceptions of zonasulcy in the eudicots, are aperture states shared exclusively with the basal dicots. Furthermore, to some extent all have links with the triaperturate condition in monocots and basal dicotyledons. This is discussed, as well as the association of tripory with polypory in monocots and basal dicots. The fossil pollen record is considered.This paper is dedicated to Klaus Kubitzki in recognition, not only for his extensive contribution to systematic botany, but also for his firm belief that pollen characteristics contribute to a better understanding of plant systematics and evolution.     

Nuclear DNA content of monocotyledons and related taxa

Nuclear DNA content of 62 species of angiosperms including 52 monocotyledons and ten dicotyledons has been estimated by flow cytometry using Nicotiana tabacum var. Xanthi as the internal standard. These data, considered together with previous data on diploid species, suggest the following: 1) Most families and orders of monocotyledons have small genomes. Contrary to the general impression that monocotyledons are a group characterized by large genomes, genomes of over 20 pg/2C nucleus occur only in the Liliiflorae, Commelinales, Alismatales, and Araceae. 2) Variation within families ranges from two- to 56-fold, but is two- to fivefold in most families. Thus extraordinary variation in genome size appears to be limited to particular lineages, perhaps owing to some shared feature that facilitates such variation. 3) Endopolyploidy is not observed in the leaves of the species studied, although it has been reported to occur in the roots of several monocotyledons. This suggests that an examination of the basis for this difference between the roots and leaves of monocotyledons may provide clues to the mechanisms that regulate endopolyploidization in these organs.     

Systematics and biology of Xylocopa subgenus Schonnherria (Hymenoptera,Apidae) in Argentina

Biological information on the species of the large carpenter bee Xylocopa subgenus Schonnherria occurring in Argentina is revised. Based on the appraisal of museum specimens, the study of type material, and field surveys conducted across 15 provinces between 2007 and 2011, the following seven species are recognized for the country: Xylocopa bambusae Schrottky, Xylocopa chrysopoda Schrottky, Xylocopa macrops Lepeletier de Saint Fargeau, Xylocopa simillima Smith Xylocopa splendidula Lepeletier de Saint Fargeau, Xylocopa pulchra Smith, and Xylocopa viridis Smith. Previous literature records of Xylocopa dimidiata Latreille, Xylocopa subcyanea Pérez, and Xylocopa varians Smith for the province of Misiones appear to have been misidentified specimens, although the presence of these species in Argentina cannot be entirely ruled out given the proximity of this province to Brazil and Paraguay where they occur; Xylocopa boops Maidl was described from a male specimen with unusually enlarged eyes and is newly synonymized under Xylocopa macrops. Males and females of all species are diagnosed, described, and figured, including details of the male genitalia. Taxonomic comments, data on the geographical distribution and nesting substrates, and identification keys to all Argentinean species of Schonnherria are provided. The nesting biologies of Xylocopa splendidula and Xylocopa viridis are documented.     

Phenolic constituents of the cell walls of monocotyledons

Monocotyledons of 104 species in 52 families were divided into two groups depending on the UV fluorescence behaviour of their cell walls. The unlignified cell walls of the first group, fluoresced blue, which changed to green with increased intensity after treatment with NH₃ due to the presence of bound ferulic acid. The isolated cell walls of members of the first group were shown to contain bound ferulic, p-coumaric and diferulic acids. These acids were absent from cell walls of the second group. The first group contained families of the Commelinidae of Cronquist, the Palmae (part of the Arecidae), and the Philydraceae, Pontederiaceae, and Haemodoraceae (all part of Liliidae). The other families of the latter two subclasses and those of the Alismatidae belonged to the second group.     

Origins and nature of vessels in monocotyledons: 8. Orchidaceae

Xylem of the orchids studied provided unusually favorable material to demonstrate how conductive tissue evolves in monocotyledons. In the end walls of tracheary elements of many Orchidaceae, remnants of pit membranes were observed with scanning electron microscopy and minimally destructive methods. The full range from tracheids to vessel elements, featuring many intermediate stages, was illustrated with SEM in hand sections of fixed roots, stems, and inflorescence axes of 13 species from four subfamilies. Pit membranes in end walls of tracheary elements are porose to reticulate in roots of all species, but nonporose in stems of Cypripedioideae and Vanilloideae and porose to reticulate in stems of Orchidoideae and Epidendroideae. The distribution pattern of pit membranes and pit membrane remnants in end walls of tracheary elements of orchids parallels the findings of others. The position of Cypripedioideae and Vanilloideae as outgroups to Orchidoideae and Epidendroideae, claimed by earlier authors, is supported by clades based on molecular studies and by our studies. Little hydrolysis of pit membranes in tracheary element end walls was observed in pseudobulbs or inflorescence axes of epidendroids. The pervasiveness of network-like pit membranes of various extents and patterns in end walls of tracheary elements in Orchidaceae calls into question the traditional definitions of tracheids and vessel elements, not merely in orchids, but in angiosperms at large. These two concepts, based on light microscope studies, are blurred in light of ultrastructural studies. More importantly, the intermediate expressions of pit membranes in tracheary element end walls of Orchidaceae and some other families of angiosperms are important as indicators of steps in evolution of conduction with respect to organs (more rapid flow in roots than in succulent storage structures) and habitat (less obstruction to flow correlated with a shift from terrestrial to epiphytic).     

Numerical analyses of distributions of Iberian and Balearic endemic monocotyledons

Chorological information concerning 182 taxa of monocotyledons endemic to the Iberian Peninsula and Balearic Islands was compiled and related to the 100×100 km, 50×50 km and 10×10 km UTM grids. Distributions were analysed using multivariate methods (two-way indicator species analysis and detrended correspondence analysis) for each scale. Comparison of results allows recognition of several floristic elements and sectors (i.e. Balearic, Murcian-Almerian, south western) common to all three scales, whereas other regions are assigned to different sectors depending on the grid size considered. As a consequence of the increase in detail, characteristics such as number of sectors, the outline of boundaries and continuity or fragmentation of the areas also change. These factors are discussed.     

A review of the fossil record of monocotyledons

The fossil record of monocotyledons is reviewed in order to determine the families actually represented by fossils and their stratigraphic ranges. In providing this information, attention is called to deficiencies and strengths in the record. Most notable is the uneven representation of the four subclasses of monocotyledons. Three distinct phases in the history of monocots can be delineated when the record and ranges of modern families are compared with paleotemperature data. First is a phase of initial radiation and diversification primarily restricted to the Cretaceous and represented by the appearance of a variety of monocotyledonous leaf forms. Second is a phase of modernization of the monocot flora resulting from further development of preexisting Cretaceous forms during favorable climatic conditions during the latest Cretaceous and Paleogene. The third phase is one marked by changes in distributions and expansion of other groups corresponding with climatic deteriorations of the late Paleogene. Some suggestions concerning the limitations of and potential for further research into the fossil record of monocots are presented.